AlertDialog widget scrollable by default (#49848)

packages/flutter/lib/src/material/dialog.dart

@@ -259,7 +259,7 @@ class AlertDialog extends StatelessWidget {
     this.insetPadding = _defaultInsetPadding,
     this.clipBehavior = Clip.none,
     this.shape,
-    this.scrollable = false,
+    this.scrollable = true,
   }) : assert(contentPadding != null),
        assert(clipBehavior != null),
        super(key: key);

packages/flutter/test/material/dialog_test.dart

@@ -1100,7 +1100,6 @@ void main() {
           color: Colors.green,
           height: 1000,
         ),
-        scrollable: true,
       );
       await tester.pumpWidget(_buildAppWithDialog(dialog));
       await tester.tap(find.text('X'));
@@ -1120,7 +1119,6 @@ void main() {
           color: Colors.orange,
           height: 1000,
         ),
-        scrollable: true,
       );
       await tester.pumpWidget(_buildAppWithDialog(dialog));
       await tester.tap(find.text('X'));
@@ -1146,7 +1144,6 @@ void main() {
           color: Colors.orange,
           height: 400,
         ),
-        scrollable: true,
       );
       await tester.pumpWidget(_buildAppWithDialog(dialog));
       await tester.tap(find.text('X'));